A. Field of Invention
This invention relates generally to a polymeric material, and more specifically to coloring of a powderous polymeric material for use in making components by melt-processing, for example by rotational molding.
Rotational molding is used for the production of hollow containers and other products of large size and complicated structure which cannot be readily molded by other conventional molding techniques such as injection molding and sheet thermoforming. Such structures include, for example, gasoline tanks, casks, storage tanks and toys.
Rotational molding includes the steps of feeding a powder comprising polymeric material to a mold, heating the mold from the exterior while rotating the mold and melting the powder, thereby forming a molten synthetic polymeric material layer within the mold, then cooling the mold to solidify the material and finally separating the mold from the molded product.
B. Description of the Related Art
To color the polymeric material powder prior to molding, it may be mixed with one or more pigments in dry powder and/or solids form. However, such solid materials can be difficult to handle and can mix unevenly with the polymeric material powder leading to inconsistent color distribution in the final molded product. Also, such a process is a time-consuming discontinuous process. Attempts have been made to use liquid color formulations. However, there are also problems associated with use of such formulations. For example, the formulations may be added during pulverization of polymeric material to produce the polymeric material powder. However, disadvantageously, this necessitates extensive and prolonged cleaning of the pulverization apparatus should it be desired to change the color of the polymeric material powder to be produced. This is generally uneconomic. Furthermore, it is challenging to homogenously color the polymeric material. It is an object of the present invention is to address the above-described problems.